This invention relates to a pick and place apparatus for transferring objects, and more particularly, a pick and place apparatus that performs suction or suction-release by opening and closing of a negative pressure source for transferring objects such as semiconductor devices.
Some applications of a pick and place apparatus for transferring objects require to transfer objects precisely and quickly in order to increase the operating efficiency of an overall system. One such example arises where a pick and place apparatus employed in a test handler incorporated with a semiconductor test system for transferring test objects. In such a test handler accompanied by a semiconductor system, the test objects to be transferred are semiconductor IC devices. Other example is a chip mounter that places various electric components in a chip form on predetermined positions of a printed circuit board and the like. This invention relates to a pick and place apparatus having a suction mechanism for attracting and releasing the objects to be transferred with a suction force produced by a negative pressure such as vacuum.
These pick and place apparatuses are required to have high efficiency to improve an overall productivity with a high transfer speed and high reliability with a low jamming rate. To achieve these objectives, in a pick and place apparatus for transferring the objects by using the suction method, a pressure detection means is provided for each suction pad for detecting the suction condition. This assures the pick-up operation (suction) by detecting the suction pressure and promotes reduction of the suction (pick-up operation) time or the suction-release (place operation) time.
An example of structure in such a pick and place apparatus is explained with reference to FIG. 5. This example controls suction and suction release operations through detection signals from a pressure detector 41. Further in this example, a plurality of devices under test (DUT) to be transferred by the pick and place apparatus are arranged on a horizontal tray.
In FIG. 5, the pick and place apparatus having suction mechanism is comprised of a suction pad 30, a pad support 32, a transfer drive means 80, a vacuum hose 38, a pressure detector 41, a negative pressure switch 45, a negative pressure source 50, and a suction controller 70.
The suction pad 30 has a pad tip 31 that contacts DUT (Device Under Test) 90, and a through-hole 75 at the center for transmitting the negative pressure to the DUT 90 therethrough. The suction pad 30 is a circular component that can pick and place the DUT by the suction force produced by the negative pressure. Examples of suction pad 30 are shown in FIGS. 6(a)-6(c). The suction pad 30 is formed, for example, with an elastic rubber pad of FIG. 6(a), or an elastic rubber pad provided with a metallic-ring cover of FIG. 6(b), or elastic rubber with a metallic pipe as shown in FIG. 6(c). The vacuum hose 38 is connected at the top of the suction pad 30 to introduce the negative pressure to the pad tip 31 through the hole 75. The negative pressure switch 45 is connected, for example, to the other end of the vacuum hose 38 for performing on/off switch operations of the suction force.
This suction pad 30 can be freely positioned by the transfer drive means 80 in three directions through the pad supporter 32. For example, the suction pad 30 is driven by the transfer drive means 80 in a vertical direction (Z) for up and down movements, and in (X-Y) directions for right and left or forward and backward movements. Such a drive means is well known in the art, such as in a robot arm technology, and thus no further explanation is given here.
The pressure detector 41 detects predetermined pressure points for evaluating a pick and place operation and initiating the next switching operation of the suction force from the negative pressure source. The pressure points to be detected vary in accordance with the length of the vacuum hose 38, contact condition between the surface of the DUT 90 and the suction pad 30, or other factors. Detection signals from the pressure detector 41 indicating the pressure points are provided to the suction controller 70.
As an example of the negative pressure source 50, an ejector vacuum pump is generally used to produce a negative pressure based on a speed of fluid caused by the release of a high-pressure air into the atmosphere. The pressure detector 41, the negative pressure switch 45 and the negative pressure source 50 may be accommodated in one module in order to minimize the overall size.
Negative-pressure curves in the vacuum hose 38 with respect to the pick operation (suction period) and the place operation (suction-release period) are shown in FIG. 4. FIG. 4(a) is a negative pressure curve in the vacuum hose during the suction period. The negative pressure in the hose 38 fluctuates between the property curves C1a and C1b. The major factors for the cause of this fluctuations are pipe lengths of the vacuum hose 38, spaces and irregularities between the suction pad 31 and the DUT 90, as well as aged deteriorations. As a result, times T1a and T1b required to reach the predetermined suction pressure point P1 are also dispersed as shown in FIG. 4(a).
FIG. 4(b) is an example showing negative-pressure property curves in the vacuum hose 38 during the suction-release period. In this example, again, dispersion in the negative pressure is shown between the property curves C2a and C2b due to the similar factors mentioned above with respect to FIG. 4(a).
In view of the pressure dispersion described above, the suction procedure to pick up the DUT 90 on the tray 100 is explained in the following. In this example, it is assumed that the suction pressure point P1 which is a negative pressure value that can reliably and certainly maintain the suction of the DUT 90 is set in the pressure detector 41.
At the beginning of the suction period, the tip of the suction pad 30 is positioned so that the suction pad 30 is lightly pressed over the DUT 90 by the transfer drive means 80. The suction controller 70 turns the negative pressure switch 45 on to introduce the negative pressure in the vacuum hose 38. This situation is illustrated in FIG. 3 which shows a pressure transition during the suction period.
In the suction period shown in the left hand side of FIG. 3, as soon as the suction pressure P1 is detected by the pressure detector 41, the suction procedure is terminated by maintaining the pressure P1. The DUT 90 is held at the tip of the suction pad and the pick and place apparatus is proceeded to the next operation, such as transferring the DUT 90 to the destined position on the test handler. In this suction procedure, the DUT 90 is reliably maintained at the tip of the suction pad 30 without any time loss.
Next, the suction release operation for releasing the DUT 90 over a predetermined position is explained. The right hand side of FIG. 3 shows the pressure transition during the suction release period. After the DUT 90 is transferred to the predetermined position, such as a seat on the tray 100 of FIG. 5, the suction controller 70 turns the negative-pressure switch 45 off to decrease the negative pressure by introducing an atmospheric pressure in the vacuum hose 38.
Since the pressure detector 41 is provided with the suction pressure point P1 as noted above, it generates a detection signal when the negative pressure in the hose 38 is reduced to the pressure point Pi, although the DUT 90 is still attracted at the tip of the suction pad 30. Thus, a timer is provided which is activated by the detection signal from the pressure detector 41. The timer is set a time length which is assumed to be appropriate to release the DUT 90 with certainty. After a signal from the timer is received by the suction controller 70, the suction release procedure is terminated and the next procedure begins.
The time length in the timer is determined by taking into consideration of the dispersion of the negative pressure for successfully releasing the DUT and an operational margin for the successful releasing operation. Thus, the time set in the timer is longer than any anticipated situations in releasing the DUT. As a result, the differences are incurred between the actual timing for releasing the DUT 90 and the time length defined by the timer, which results in waste of time. On the other hand, if the time length is set to be shorter, a jamming of DUTs may occur and transfer reliability may be degenerated.